The invention relates to circuit integrity in a packet-switched network.
System Signal 7 (SS7) messages are often used to provide control signals in various telecommunications systems, such as telephone systems, and provide a mechanism, known as continuity check, for checking the integrity of a circuit between two switching network endpoints during call setup. Continuity checks originally were developed for analog facilities and consist, for example, of a frequency tone transmitted by the originating exchange and looped back by the receiving exchange. Reception of the returned tone by the originating exchange indicates that the channel is available. In digital environments, use of continuity check operations has been similar.
Recently, packet-domain network architectures, such as asynchronous transfer mode (ATM) networks, have been considered for transporting voice and other narrowband traffic. Packet networks allow connections to be made between endpoints without dedicated inter-switch connections. Fixed-size packets of data, known as cells, are transferred between the ATM switches, which are packet switches that provide virtual circuits between the end points of a network.
With the advent of packet voice networks and the introduction of adaptation between circuit-switched and packet-switched bearers, high-quality integrity checks should be capable of detecting and isolating various types of failures. Traditional testing by continuity check tones, however, is incapable of detecting certain failures such as, for example, impaired bits having low significance with respect to a time-domain multiplexed (TDM) sample value. Therefore, better-quality continuity checking suitable to packet networks is desirable.